FDA Slaps Clinical Hold on BioMarin's Gene Therapy For Genetic Metabolism Disorder

BioMarin Pharmaceutical Inc BMRN faces another setback in its gene therapy development program after the FDA placed the phenylketonuria (PKU) gene therapy trial on hold.
The Phase 1/2 Phearless study is evaluating BMN 307, an AAV5-phenylalanine hydroxylase (PAH) gene therapy for PKU.
PKU is a rare genetic disease that manifests at birth and is characterized by an inability to break down phenylalanine, an amino acid commonly found in many foods.
The agency ordered the pause on the study after liver tumors were seen in mice given the therapy in preclinical testing.
BioMarin’s preclinical study was carried out to explore the durability of BMN 307 activity in mice with two germline mutations that may predispose them to cancer development.
One mutation eliminated the PAH gene that’s missing in PKU, while the second rendered the animals immunodeficient, which could also raise the risk of malignancy.
Of 63 animals treated, six of seven animals administered BMN 307 at the highest dose group – 2e14 Vg/kg – developed liver tumors.
Five of the mice had adenomas, and one had hepatocellular carcinoma.
So far, participants have received doses of either 2e13 vg/kg or 6e13 vg/kg of BMN 307, although the protocol does include a third, higher-dose group.
Read Next: Drug For Short-Limbed Dwarfism From Biomarin Wins European Approval.
The clinical hold for the PKU program comes after BioMarin’s hemophilia A gene therapy was rejected by the FDA last summer.
The rejection would delay the approval by around two years, as the FDA asked for two-year data on all study participants.
The last patient will complete two years of follow-up in November 2021.
Related content: Benzinga's Full FDA Calendar.
Price Action: BMRN shares closed at $84.95 on Friday.

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